360 Weed and Pirsson — Bearjpaw Mountains, Montana. 



I. 



Si0 2 50-00 



Al 2 O s 9-87 



Fe 2 3 3-46 



FeO 501 



MgO 11-92 



CaO 8-31 



Na 2 2-41 



K 2 0.___ 5-02 



Ti0 2 -73 



H 2 0-llO°_-.. -IV 



H 2 O + 110° 1-16 



Cr.O, -_- -11 



MnO trace 



NiO -.-. -07 



BaO -32 



SrO-..- '07 



Fl -16 



CaC0 3 ._.. 



CI -08 



PA '81 



SO a -02 



C0 2 -31 



Li„0 trace 



= C1 &F1 



100-01 

 •08 



II. 



48-98 



12-29 



288 



5-77 



9-19 



9-65 



2-22 



4-96 



1-44 



•26 



•56 



trace 



•08 



•43 



•08 

 •22 



■98 



trace 



99.99 

 •08 



III. 



46-73 



1005 



3-53 



8*20 



9-68 



13-22 



1-81 



3-76 



•78 



•28 



undet. 

 undet. 



•18 



1-51 



trace 



trace 



100-97 

 •04 



IV. 

 50-43 

 10-21 



11-57 



5-58 



14-82 



1-48 



3-70 



? 



•87 



9 

 ? 



•52 



•70 



99.88 



la. 

 8333 

 0958 

 0216 

 0696 

 2980 

 1484 

 0388 

 0532 



99-93 9991 100-93 



I. Shonkinite, Beaver Creek, Bearpaw Mountains, H. N. 

 Stokes anal. 



II. Shonkinite, Yogo Peak, Little Belt Mountains, Montana. 

 W. F. Hillebrand anal. 



III. Shonkinite, Square .Butte, High wood Mountains, Montana, 

 L. V. Pirsson a'nal. 



IV. Shonkinite, Monzoni (Lemberg, Zeitschr. d. deutsch. G. G., 

 1872, p. 201), Lemberg anal. 



la. Molecular proportions in No. I. 



It will be seen in the above that the rock has all the char- 

 acters of the type, high, lime, iron, and magnesia and also high 

 alkalies with potash dominating the soda. We have introduced 

 the analyses of the previous types described by us and also one 

 of a pyroxene-orthoclase rock from Monzoni, being indebted to 

 Brogger* for the reference. It should evidently fall under 

 this type. 



Broggerf remarks that shonkinite is " a peculiar pyrox- 

 enite rich in plagioclase " ; this is certainly true, but the same 



* Eruptionsfolge eruptivgesteine Predazzo, 1895, p. 66. 

 f Loc. cit. 



